1. Field of the Invention
The present invention relates to an exhaust passage of an exhaust gas (combustion gas) discharged from an exhaust port of an engine mounted in a small watercraft such as a personal watercraft (PWC), and a water muffler provided at a downstream portion of the exhaust passage in a flow of the exhaust gas.
2. Description of the Related Art
In recent years, jet-propulsion personal watercraft, which is one type of small watercraft, have been widely used in leisure, sport, rescue activities, and the like. The personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a bottom hull surface and ejects it rearward from an outlet port. As the resulting reaction, a body of the jet-propulsion personal watercraft is propelled. In the jet-propulsion personal watercraft, a steering nozzle provided behind the outlet port of the water jet pump is swung either to the right or to the left by operating a bar-type steering handle to the right or to the left, to change the ejection direction of the water to the right or to the left, thereby turning the watercraft to the right or to the left.
A first exhaust pipe fixed to the engine and a second exhaust pipe connected to the first pipe and including a muffler extending to muffle and discharge an exhaust gas from the engine outside the watercraft belong to different vibration systems, and are connected to each other through a rubber tube. However, since the rubber tube is exposed to a high temperature exhaust gas, durability of the rubber tube is reduced. Therefore, it is necessary to form a water supply hole in a portion upstream of a connecting portion of the exhaust pipes where the rubber tube is provided to allow a temperature of the exhaust gas to be reduced by supplying water to the exhaust gas. This is called “wet type.” When the “wet type” is adopted in the connecting portion, water is reserved within the exhaust passage during a stopping state of the engine, while, during re-starting of the engine, the water within the exhaust passage might flow back toward a combustion chamber of the engine.
Since the personal watercraft is as short as approximately 3 to 4 m in total length, and the engine is located at substantially the center portion of the watercraft, the total length of the exhaust passage cannot be extended. In order to gain a peak output at a low engine speed of the engine in the personal watercraft having such a short exhaust passage, a water jacket is typically provided around the exhaust passage to allow a temperature of the exhaust gas to be reduced. In addition, water mist is supplied into the muffler to reduce the temperature of the exhaust gas for enhanced muffling effect. This is called “water muffler.” However, during a stopping state of the engine, the water is reserved in the bottom portion of the water muffler and, during re-starting of the engine, the water reserved in the bottom portion might be suctioned toward the engine. Further, when the watercraft is inverted, the water outside the watercraft might enter the water muffler.